Plant growth substrates

ABSTRACT

A man-made vitreous fibre (MMVF) plant growth substrate is provided together with an irrigation strategy for providing water to the substrate. The substrate comprises a slab having a volume of 3 to 20 litres on which a single block containing one or more plants is disposed. In the context of this substrate, it is found that an irrigation strategy can be used which comprises a first period during which the desired water content in the slab is reduced to a minimum level before increasing and a second period during which the desired water content is maintained at a substantially constant level, wherein the difference between the minimum level and the constant level expressed as a percentage of the water content required to saturate the plant growth substrate is less than or equal to 25%. This provides excellent control over the balance between vegetative and generative growth in the plant.

FIELD OF THE INVENTION

The present invention relates to the growth of plants in artificialsubstrates. In particular, but not exclusively, the present inventionrelates to the growth of plants in mineral wool substrates.

BACKGROUND TO THE INVENTION

It is known that plants can be grown in mineral wool growth substrates.Such growth substrates are typically provided as a coherent plug, block,slab or mat/blanket and generally include a binder, usually an organicbinder, in order to provide structural integrity to the product.

Typically, the growth process of the plant is managed in two stages: afirst stage managed by a “propagator” in which the plant is grown fromseed; and a second stage managed by a “grower” during which the plant issustained and any harvest taken. For example, in the case of the tomatoplant, the propagator may plant individual tomato seeds in cylindricalplugs having a thickness in the order of 25-30 mm and a radius of around20-30 mm. After germination of the seed, the propagator places the plugwithin a cuboid block to allow further growth of the root system and theplant. The individual plant within the block is then nursed until astage when it can be transferred from the propagator to the grower.

Although typically only a single plant is provided in each block, it ispossible for multiple plants to be provided in a single block. In someexamples, a single plant in a block is split into two by splitting astem during an early phase of growth, resulting in two plants sharing asingle root system. In another alternative, multiple plants may begrafted together and grown within a single block.

The use of a separate plug and block by the propagator is not essentialfor all plants, but has been described, for example, in European patentapplication EP2111746, as providing a number of advantages. Inparticular, the small size of the plug allows more regular watering ofthe plant in the initial stage without saturating its substrate.

After they are received from the propagator, the grower places a numberof blocks on a single slab of mineral wool to form a plant growthsystem. The slab of mineral wool is typically encased in a foil or otherliquid impermeable layer except for openings on an upper surface forreceiving the blocks with the plants and a drain hole provided on thebottom surface.

During subsequent growth of the plant, water and nutrients are providedusing drippers which deliver a liquid containing water and nutrients tothe system either directly to the blocks or to the slabs. The water andnutrients in the blocks and slabs is taken up by the roots of the plantsand the plants grow accordingly. Water and nutrients which are not takenup by the plant either remain in the substrate system or are drainedthrough the drain hole.

There is a desire to use water and nutrients as efficiently as possibleduring the growing process. This is both for cost and environmentalreasons. In particular, the nutrients are expensive to obtain, whilewaste water containing such nutrients is difficult to dispose of due toenvironmental legislation. The desire to avoid such waste is matched bya desire to improve plant growth conditions, and thereby to increase theyield and quality of fruit obtained from plants in this manner.

The use of mineral wool itself provides significant benefits in thisregard as compared to traditional soil-based growing methods, but thereis an ongoing requirement to further improve these characteristics. Inparticular, there is a conflicting desire to both produce more andconsume less in plant growth processes. That is, a greater yield fromthe plants is desired while at the same time reducing the amount ofwater and/or nutrients that are used. In practice, existing growingmethods and/or substrates provide limitations on both these aspects.

In nature, plant growth can be understood and divided into two distinctphases: vegetative growth and generative growth. During vegetativegrowth, the plant predominantly grows leaves and other green elementswhich enable it maximise its photosynthetic potential. During thegenerative growth stage the plant predominantly starts to set and growfruits. A higher proportion of growth during a generative phase isdirected towards flowers and fruit, while the absolute overall biomassgrown during a vegetative phase is higher but is predominantly directedto leaves.

It is known that whether a plant enters a generative growth phase or avegetative phase depends in large part on the water and nutrients theplant receives or has access to within the substrate. In particular,when the plant is stressed (i.e. when it receives relatively littlewater and/or nutrients) generative growth begins whereas when the plantis provided with plentiful water and/or nutrition vegetative growthbecomes predominant.

In view of this, it is known to “steer” plants towards vegetative orgenerative growth by adopting an irrigation strategy in which the amountof water provided to the plant varies. For example, in practice, themineral wool slab described above may typically be saturated prior tothe placement of the plant-containing block upon the surface of theslab. This is in order to ensure that the roots from the plant in theblock are encouraged to grow into the slab.

Once the block has been placed on the slab, it is known for the growerto attempt to apply a “generative impulse” to the plant by reducing thewater content of the slab. The grower is keen for the plant to flower(and thus provide fruit) as soon as possible in order to obtainproducts/fruits which can be sold. Once this process is initiated,however, the grower wishes to encourage the overall growth of the plant.To do so, the grower then increases the water content in the slab to alevel appropriate for vegetative growth. Thus, the grower steers theplant between vegetative growth and generative growth.

However, in practice, the steering of plant growth in this manner iscrude and inefficient. In particular, the grower does not have accuratecontrol over the overall water content in each slab, and moreover thereare typically wide variations in the water content within the slab (forexample, the water content is typically higher at the bottom of the slabthan at the top). It is found in this context that to achieve agenerative impulse having the desired effect, the water content levelduring the generative impulse must be significantly lower than thatrequired during a subsequent continuous growth phase.

One attempt to improve the distribution of water and nutrients in asubstrate is described in European patent application EP0300536. In thisdocument, a system is described in which multiple blocks are provided ona single slab and a capillary system is used to apply a constant suctionpressure across the slab. The aim of this suction pressure is to drawmore water in to areas that become relatively dry, thereby increasingthe uniformity of the water distribution across the slab.

In practice, there are a number of drawbacks with the system describedin EP0300536. In particular, while there may be some benefit in terms ofthe uniformity of the water distribution across the slab in thehorizontal plane, this does not provide significant benefits in terms ofthe vertical variation in water content that has been found. Moreover,the system of EP0300536 is relatively expensive to implement.

Using conventional techniques, there remain significant difficulties insteering plant growth between generative and vegetative states. The lackof uniformity within the slab means that the true plant growthconditions cannot be closely controlled. Moreover, the control that ispossible is cumbersome, requiring a significant time period to transferbetween a generative impulse and a subsequent sustainable growth state.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda plant growth method, comprising:

-   -   providing a plant growth substrate comprising an MMVF slab        having a volume in the range 3 to 20 litres and a single MMVF        block containing one or more plants on a first surface of the        MMVF slab;    -   providing the plant growth substrate with water during growth of        the one or more plants according to an irrigation strategy which        defines a desired water content in the slab,    -   wherein the irrigation strategy comprises a first period during        which the desired water content is reduced to a minimum level        before increasing and a second period during which the desired        water content is maintained at a substantially constant level,    -   wherein the difference between the minimum level of the first        period and the constant level of the second period expressed as        a percentage of the water content required to saturate the plant        growth substrate is less than or equal to 25%.

The plant growth method of the present invention can utilise thesurprising discovery that the growth of plants on a single block placedon a slab of a relatively small size can allow an effective generativeimpulse to be applied to the plant during a first period at a watercontent value which is relatively close to that required for a latersteady growth state during a second period. The small difference betweenthe required water content levels for different phases of the irrigationprocess reduces multiple problems that may occur in previous approaches.In particular, the transition from the minimum level to the constantlevel can be carried out relatively quickly, thus improving the controlover the steering of the plant. Moreover, in prior art techniquessignificant amounts of water and/or nutrients are typically spilled fromthe slab when the water level is increased, whereas such problems areless apparent in the present invention. The man made vitreous fibres(MMVF) of the present invention may be fibre glass, mineral wool orrefractory ceramic fibres. In preferred embodiments, the MMVF is mineralwool.

Preferably, the difference between the minimum level and the constantlevel expressed as a percentage of the water content required tosaturate the plant growth substrate is less than or equal to 20%, andmore preferably less than 15%. In particularly preferred embodiments,this difference is in the range 10% to 15%. These relatively smallvalues improve the control over the steering of the plant growth.

Preferably, the minimum level expressed as a percentage of the watercontent required to saturate the plant growth substrate is at least 50%.It is found that the minimum level does not have to be reduced belowsuch a value. This makes it relatively easy and quick to achieve theminimum level. More preferably, the minimum level expressed as apercentage of the water content required to saturate the plant growthsubstrate is at least 60%.

Preferably, the constant level during the second period expressed as apercentage of the water content required to saturate the plant growthsubstrate is 75% or less. Avoiding a high constant level minimises thepossibility of saturation of the substrate, and allows the balancebetween generative and vegetative growth to be closely controlled.

As mentioned above, one of the benefits of the approach of the inventionis the speed at which preferred water levels can be safely reached. Inparticular, the desired water content is preferably reduced to theminimum level within 7 weeks of commencement of the irrigation strategy.Moreover, the desired water content preferably reaches the substantiallyconstant level within 12 weeks of commencement of the irrigationstrategy. By achieving these values sooner than is safely possible inthe prior art, the present invention allows desired generative orvegetative plant growth to be initiated sooner, and, for example, thegrower to provide fruit to market sooner than previously possible.

Preferably, the irrigation strategy further comprises a third periodduring which the desired water content is reduced. Accordingly, after aperiod of sustainable growth during the summer months, the balancebetween vegetative and generative conditions is tipped towards thelatter, encouraging the growth of fruit towards the end of the normalgrowing season once the plant is well established.

In preferred embodiments, the method further comprises providingnutrients to the plant growth substrate. Preferably, the step ofproviding nutrients to the plant growth substrate is carried out independence on a monitored nutrient level within the plant growthsubstrate.

In preferred embodiments, the step of monitoring the nutrient content ofthe slab comprises monitoring the electrical conductivity of fluidwithin or drained from the slab. The electrical conductivity of fluidgives an indication of the amount of salt ions (originating with theapplied nutrients of fertilisers) within the fluid. This is typicallyindicative of the nutrient level in the fluid.

In preferred embodiments, the substrate comprises a hydrophilic bindingsystem and/or a binding system comprising an organic binder selectedfrom formaldehyde free binders. The binding system may comprise thebinder and a wetting agent, or may comprise the binder alone. Byensuring that the binding system is hydrophilic, the water retentionproperties of the slab can be improved relative to binding systems whichare non-hydrophilic or hydrophobic.

Preferably, the binder comprises the reaction product of apolycarboxylic acid component and a polyol and/or an amine component,preferably in admixture with a sugar component and/or a phenol. Morepreferably, the binder is a reaction product of a polycarboxylic acid oranhydride thereof, an amine, preferably an alkanolamine, and a sugar,preferably a reducing sugar. These binders are found to offerparticularly advantageous properties in MMVF slabs.

The wetting agent preferably comprises an ionic surfactant distributedin one or both said layers. Preferably, the surfactant is an anionicsurfactant, preferably a sulphonate surfactant, preferably linear alkylbenzene sulphonate (LABS). These preferred wetting agents have beenfound to offer beneficial effects, particularly improving thehydrophilicity of the binder system.

Preferably, the substrate further comprises a liquid impermeablecovering surrounding the MMVF block, wherein the drain hole is formed bya first aperture in said covering and the MMVF block contacts the MMVFslab through a second opening in said covering. The liquid impermeablecovering allows the majority of liquid to be retained in the slab asdesired, while allowing additional liquid and drainage to occur

Preferably, the MMVF slab comprises a first layer of MMVF in interfacialcontact with a second layer of MMVF, the first layer having a greaterdensity than the second layer. The provision of separate densities hasbeen found to increase control over the distribution of water andnutrients in the substrate. In preferred embodiments, the first layer ofMMVF has a density in the range 40 to 90 kg/m³ and the second layer ofMMVF has a density in the range 35 to 85 kg³. More preferably, thedensity of the first layer is in the range 50 kg/m³ to 80 kg/m³ and/orthe density of the second layer is in the range 45 kg/m³ to 75 kg/m³. Ina particularly preferred embodiment, the density of the first layer is70 kg/m³ and the density of the second layer is 50 kg/m³. Thesedensities are found to offer good properties for plant growth, includingwater and nutrient retention.

The density of the second layer is less than that of the first layer.Preferably, the density of the second layer is at least 5 kg/m³ lessthan that of the first layer, more preferably at least 10 kg/m³, andmost preferably around 20 kg/m³. This contrast between the densities ofthe layers assists in ensuring that water and nutrients are suitablydistributed through the slab, and in particular can help to avoid anexcessive proportion of water and/or nutrients being found in the secondlayer.

In preferred embodiments, the thickness of the first layer is less thanthe thickness of the second layer. Preferably, the thickness of thefirst layer is approximately half the thickness of the second layer.These proportions are found to assist in maintaining a preferreddistribution of water and nutrients in the slab.

In preferred embodiments, the predominant fibre orientation of the firstand second layers is horizontal. In this context, horizontal meansparallel to the interfacial contact between the first and second layers.In other preferred embodiments, the predominant fibre orientation of oneor both of the first and second layers is vertical (i.e. perpendicularto the interfacial contact). For example, in a particularly preferredembodiment, the predominant fibre orientation of the first layer isvertical while the predominant fibre orientation of the second layer ishorizontal. The fibre orientations can affect the flow speed of liquidthrough the slab. For example, horizontal fibre orientations can reducethe flow speed of liquid through the slab and have a consequentbeneficial effect on the amount of liquid that is spilled.

The MMVF block is preferably provided in contact with the first layer.Moreover, the first layer is preferably above the second layer in use.Furthermore, water and nutrients are preferably provided to the block orto the first layer. In this way, water and nutrients may be received inthe first, more dense layer. This has been found to offer good waterretention and distribution properties.

In preferred embodiments the block has a volume in the range of 50ml-5000 ml and/or each block a density in the range of 30 kg/m³-150kg/m³. These sizes and densities have been found to be effective for usein plant growth systems.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings, in which:

FIG. 1 illustrates a slab used for plant growth in accordance with apreferred embodiment of the present invention;

FIG. 2 illustrates a plant growth system comprising a block togetherwith the slab of FIG. 1;

FIG. 3 illustrates the block of FIG. 2 together with a plug and a plant;

FIG. 4 illustrates an irrigation device in place next to the plantgrowth system of FIG. 2;

FIG. 5 illustrates the location of water and nutrient detectors on theplant growth system of FIG. 2;

FIG. 6 shows schematically a plant growth control system comprises aplurality of the plant growth systems of FIG. 2;

FIG. 7A illustrates the progression of a desired water level in the slabin a conventional irrigation strategy;

FIG. 7B illustrates the progression of a desired water level in the slabin an irrigation strategy in accordance with a preferred embodiment ofthe present invention;

FIG. 8A illustrates the volume of water and nutrient solution applied toan array of nine plant growth systems daily during a new irrigationstrategy in accordance with the present invention and a conventionalirrigation strategy;

FIG. 8B illustrates the accumulated daily drain of the array of nineplant growth systems during a new irrigation strategy in accordance withthe present invention and a conventional irrigation strategy;

FIG. 8C illustrates the number of trickle sessions each day and thevolume of water and nutrient solution applied during each tricklesession for a new irrigation strategy in accordance with the presentinvention and a conventional irrigation strategy;

FIG. 8D provides a table summarising the results of FIGS. 8A to 8C;

FIG. 9 illustrates an achieved water content level in a plant growthsubstrate over a long term study;

FIG. 10A illustrates a prior art plant growth system;

FIG. 10B illustrates a preferred embodiment of a plant growth systemaccording to the present invention;

FIG. 11 shows the variation in the measured water content and electricalconductivity for the preferred embodiment of FIG. 10B and the prior artof FIG. 10A under both preferred and conventional irrigation strategies;

FIG. 12 shows a comparison of the achieved yield of red fruit for thepreferred embodiment of FIG. 10B and the prior art of FIG. 10A for bothpreferred and conventional irrigation strategies;

FIG. 13A illustrates total production over the long term study for firstand second preferred embodiments of the present invention and for aprior art plant growth substrate;

FIG. 13B illustrates the results shown in FIG. 13A using the productionof the prior art plant growth substrate as a base figure;

FIG. 14 compares the rate of change of the EC level of a slab for apreferred embodiment of the present invention and a prior art approachwhen a solution having a different EC level to that initially present inthe slab is introduced by irrigation;

FIG. 15A illustrates the EC level at different points of a slab when ablock is located towards the drain hole; and

FIG. 15B illustrates the EC level at different points of a slab when ablock is located away from the drain hole.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown a mineral wool slab 1 having a firstlayer of a first density disposed above a second layer of a seconddensity. The slab 1 has a volume of 6.8 litres, although more generallythe volume may be in the range of 3 litres to 20 litres, more preferablyin the range 5 litres to 15 litres, and most preferably in the range 5to 11 litres. Some embodiments comprise a slab with a volume in therange 6 litres to 8 litres. In other embodiments, the volume may lie inthe range of 3 litres to 15 litres, or 3 litres to 10 litres, forexample. An alternative preferred embodiment comprises a slab having avolume of 9 litres.

The height h of the slab 1 of FIG. 1 is 100 mm, although more generallyit may lie between 75 mm to 150 mm and more preferably between 85 mm and125 mm. The width w of the slab 1 is 150 mm, although this may moregenerally lie in the range of 100 mm to 300 mm, for example. Thelength/of the slab 1 is 450 mm, although this value may also be varied,and may, for example, lie in the range of 200 mm to 800 mm, orpreferably in the range 250 mm to 600 mm. A particular preferredembodiment comprises a slab 1 having a height h of 100 mm, a width w of150 mm and a length l of 600 mm.

In the preferred embodiment shown in FIG. 1, the first layer has aheight a of 40 mm and a density of 70 kg/m³ while the second layer has aheight b of 60 mm and a density of 50 kg/m³. Again, in other preferredembodiments different values of these parameters may be chosen. Forexample, the height a of the first layer may lie in the range of 25 mmto 50 mm, while the height of the bottom layer may lie in the range of50 mm to 100 mm. Similarly, the density of the top layer is preferablyin the range of 40 kg/m³ to 90 kg/m³, more preferably 50 kg/m³ to 80kg/m³, while the density of the bottom layer is preferably in the rangeof 35 kg/m³ to 85 kg/m³, more preferably 45 kg/m³ to 75 kg/m³.

As is the case in the embodiment shown in FIG. 1, it is preferable thatthe height of the bottom layer is greater than that of the top layer.For example, the ratios between the heights of the top and bottom layersmay be 1:(1-3), or preferably 1:(1.2-2.5). More preferably, this ratiois 1:(1.2-1.8).

The use of two differing densities in the slab of the preferredembodiment, together with its relatively small size, have been found toassist in the retention of water and nutrients and also ensuring thatthese are distributed substantially uniformly throughout the slab.

This can be seen, for example, in Table 1 below. Table 1 illustrates theresponse of various slabs having dimensions of 450 mm*150 mm*100 mm andcomprising two layers of differing density as described above. The slab1 of Column A has a top layer of height 30 mm and a bottom layer ofheight 70 mm; the slab 1 of Column B has a top layer of height 40 mm anda bottom layer of height 60 mm; and the slab 1 of Column C has top andbottom layers both of height 50 mm.

TABLE 1 Column A Column B Column C Uniformity WC  13  9  8 within (%)Reaction time EC 5.0 −> 3.2 −> 5.0 −> 2.9 −> 5.0 −> 3.3 −> 2.5 −> 2.12.7 −> 2.1 2.7 −> 2.3 Irrigation 100 100 100 efficiency (%)

Various properties of each slab were analysed, including uniformity ofwater content (uniformity WC level) and the reaction when a change of ECwas introduced (reaction time EC). It was found that the slabs ofColumns A and B demonstrated improved EC reaction time, while WCuniformity was observed to be improved for the slabs of Columns B and C.Given the desirability of close control of nutrient content (i.e.improved EC reaction time) and uniform WC, the slab of Column B wasconsidered optimum of the examples shown. The ratio between the heightsof the top and bottom layers of 1:1.5 exhibited by this slab fallswithin the preferred range of 1:(1.2-1.8).

Reaction time EC in Table 1 is measured as follows. Firstly, the slabsare saturated at 60% water content with an EC of 5. Subsequently, theslabs are irrigated in turns with 264 ml of EC2 solution per turn on theslab. The EC within the slab is measured after 0, 9, 17 and 32 turns.Accordingly, in the case of Column A, for example, the results are asfollows: 0 turns applied—EC 5; 9 turns applied—EC 3,2; 17 turnsapplied—EC 2,5; and 32 turns applied—EC 2,1.

Referring now to FIG. 2, the slab 1 is shown with a block 2 positionedon its upper surface. The slab 1 further comprises a liquid impermeablecovering around the mineral wool, the covering having two openings.Firstly, there is an opening on the upper surface to allow contactbetween the mineral wool of the slab 1 and the block 2. Secondly, thereis an opening on a lower surface which acts as a drain hole 3.

As can be seen in FIG. 2, the slab 1 is associated with only a singleblock 2 for containing plants. In this way, the environment of the plantor plants in a single block 2 can be directly managed more effectively.This contrasts with previous systems in which a plurality of blocks 2 isprovided on each slab 1. In particular, this avoids interference betweenplants from different blocks 2 and consequent inconsistency in water ornutrient supplies to such plants.

Whereas the block 2 is provided on an upper surface of the slab 1, thedrain hole 3 is provided at or adjacent to an edge of a lower surface ofthe slab 1. The position of the block 2 as measured from its centralpoint is preferably offset from that of the drain hole 3 by a distance xalong the lengthy of the slab 1. The distance x is preferably greaterthan 50% of the length l of the slab 1, more preferably greater than 60%of this length, and may be greater than 70% of this length, althoughmost preferably it is between 65% and 70%. In the particular preferredembodiment shown in FIG. 2, the block 2 is offset from the position ofthe drain hole 3 by around 66.7% of the length of the slab.Specifically, the length l of the slab 1 is 450 mm, while the block 2 isplaced at a distance of 300 mm from the end of the slab 1 on which thedrain hole 3 is disposed. By increasing the distance between the block 2and the drain hole 3, the path length of solution comprising water andnutrients provided to or adjacent to the block is increased. This isfound to provide benefits in terms of the nutrient refreshmentefficiency of the slab 1.

The block 2 and the slab 1 are preferably formed of the same or asimilar material. Thus the description below regarding the material ofthe slab 1 may equally be applied to the block 2. In particular, theblock 2 may comprise stone wool and the binders and/or wetting agentsdescribed below. In the preferred embodiment, the block 2 has a volumeof 1200 ml. More generally the block may have a volume in the range of50 ml to 5000 ml, more preferably 100 ml to 3500 ml, more preferably 250ml to 2500 ml, and most preferably 100 ml to 2000 ml. The overall volumeof the combination of the slab 1 and block 2 is preferably in the rangeof 6 to 13 litres.

The block dimensions can be chosen in dependent on the plant to begrown. For example, the preferred length and width of a block for pepperor cucumber plants is 10 cm. For tomato plants, the length is increasedto 15 cm. The height of the blocks is preferably in the range of 7 to 12cm, and more preferably in the range of 8 to 10 cm.

Therefore, preferred dimensions for pepper and cucumber range from 10cm*10 cm*7 cm to 10 cm*10 cm*12 cm, and more preferably from 10 cm*10cm*8 cm to 10 cm*10 cm*10 cm. In terms of volume, therefore, thepreferred range is 0.7 litres to 1.2 litres, more preferably 0.8 litresto 1 litre for cucumber and pepper plants. For tomato plants, thepreferred dimensions range from 10 cm*15 cm*7 cm to 10 cm*15 cm*12 cm,and more preferably from 10 cm*15 cm*8 cm to 10 cm*15 cm*10 cm. In termsof volume, therefore, the preferred range is 1.05 litres to 1.8 litres,more preferably 1.2 litres to 1.5 litres for tomato plants. The overallrange of volumes for these crops is therefore preferably 0.7 litres to1.8 litres, and more preferably 0.8 litres to 1.5 litres.

The density of the block 2 is preferably in the range of 30 kg/m³ to 150kg/m³, more preferably in the range of 40 kg/m³ to 120 kg/m³, and mostpreferably in the range of 50 kg/m³ to 100 kg/m³. The height of a block2 is preferably in the range 50 mm to 160 mm, more preferably in therange 60 mm to 125 mm and most preferably in the range 80 mm to 100 mm.The length and width of the block 2 may independently vary in the range50 mm to 250 mm, preferably in the range 60 mm to 200 mm, and mostpreferably in the range 70 mm to 150 mm. These sizes and densities havebeen found to be effective for use in plant growth systems.

FIG. 3 illustrates a plant 5 in position within a plug 4 disposed withina block 2, such as that shown in FIG. 2. Like the block 2, the plug 4 istypically formed of a mineral wool with a binder and/or wetting agent asdescribed below in the context of the slab 1. The plug 4 is preferablycylindrical with a diameter of 20 mm to 50 mm, preferably 20 mm to 40mm, and a height of 20 mm to 50 mm, preferably 25 mm to 35 mm.

Each block 2 may in a preferred embodiment contain a single plant 5.However, it is possible that multiple plants 5 may be provided for eachblock 2, either by providing multiple plugs 4 each containing a singleplant 5 or providing multiple plants in a single plug 4. In otherpreferred embodiments, a single plant is divided into two by splittingthe stem of the plant at an early stage of growth.

In some embodiments, the plug 4 is not provided, and the seed isdisposed directly within a hole in the block, from which the plant 5subsequently grows. An example of a plant for which this approach istaken is the cucumber.

Preferably, the plant 5 is fruit or vegetable plant, such as a tomatoplant or the like. In other preferred embodiments, the plant is acucumber, aubergine or sweet pepper plant. The preferred embodiments ofthe present invention can increase the yield of fruit or vegetables froma plant and may also increase the quality of that fruit or vegetable.

As mentioned above, the slab 1 is a mineral wool slab. The mineralfibres employed may be any man-made vitreous fibres (MMVF), such asglass fibres, ceramic fibres, basalt fibres, slag wool, stone wool andothers, but are usually stone wool fibres. Stone wool generally has acontent of iron oxide at least 3% and content of alkaline earth metals(calcium oxide and magnesium oxide) from 10 to 40%, along with the otherusual oxide constituents of mineral wool. These are silica; alumina;alkali metals (sodium oxide and potassium oxide) which are usuallypresent in low amounts; and can also include titania and other minoroxides. In general the product can be formed of any of the types ofman-made vitreous fibre which are conventionally known for production ofgrowth substrates.

The mineral wool is typically bound by a binding system which comprisesa binder composition and additionally a wetting agent. In the preferredembodiment, the slab comprises mineral wool bound by a bindercomposition which, prior to curing, comprises: a) a sugar component, andb) a reaction product of a polycarboxylic acid component and analkanolamine component, wherein the binder composition prior to curingcontains at least 42% by weight of the sugar component based on thetotal weight (dry matter) of the binder components.

This composition is included in the mineral wool which is to be used forthe slab 1 and then cured, so that in the slab shown in FIG. 1 thecomposition has been cured and so the components will have reacted. Thusthe slab contains a cured binder obtained by curing of the definedbinder composition containing components (a) and (b) and the componentsof the binder composition discussed below refer to the composition priorto curing.

The sugar component (a) employed in accordance with the presentinvention is preferably selected from sucrose and reducing sugars ormixtures thereof.

A reducing sugar is any sugar that, in solution, has an aldehyde or aketone group which allows the sugar to act as a reducing agent. Inaccordance with the present invention, reducing sugars may be present inthe uncured binder composition as such or as a carbohydrate compoundthat yields one or more reducing sugars in situ under thermal curingconditions. The sugar or carbohydrate compound may be monosaccharide inits aldose or ketose form, a disaccharide, a triose, a tetrose, apentose, a hexose, or a heptose; or a di-, oligo- or polysaccharide; orcombinations thereof. Specific examples are glucose (i.e. dextrose),starch hydrolysates such as corn syrup, arabinose, xylose, ribose,galactose, mannose, fructose, maltose, lactose and invert sugar.

Component (b) essentially comprises a reaction product of apolycarboxylic acid component and an alkanolamine component.

Preferably the alkanolamine component is selected from diethanolamine,triethanolamine, diisopropanolamine, triisopropanolamine,methyldiethanolamine, ethyldiethanolamine, n-butyldiethanolamine,methyldiisopropanolamine, ethyl-isopropanolamine,ethyldi-isopropanolamine, 3-amino-1,2-propanediol,2-amino-1,3-propanediol and tris(hydroxymethyl)aminomethane. Mostpreferably the alkanolamine component is diethanolamine.

In the binder composition which is used in the products of the inventionit is preferred to have the reaction product (b). However, in practicethere is usually also some unreacted alkanolamine component present inthe uncured binder composition.

The polycarboxylic acid component is generally selected fromdicarboxylic, tricarboxylic, tetracarboxylic, pentacarboxylic, and likepolycarboxylic acids, and anhydrides, salts and combinations thereof.

Preferred polycarboxylic acid components employed as starting materialsfor reacting with the other binder components are carboxylic anhydrides.

In the binder composition which is used in the products of the inventionit is preferred to have the reaction product (b). However, in practicethere is usually also some unreacted polycarboxylic acid componentpresent in the uncured binder composition.

In order to improve the water solubility and dilutability of the binder,a base may be added up to a pH of about 8, preferably a pH of betweenabout 5-8, and more preferably a pH of about 6. Furthermore, theaddition of a base will cause at least partial neutralisation ofunreacted acids and a concomitant reduction of corrosiveness. Normally,the base will be added in an amount sufficient to achieve the desiredwater solubility or dilutability. The base is preferably selected fromvolatile bases which will evaporate at or below curing temperature andhence will not influence curing. Specific examples of suitable bases areammonia (NH₃) and organic amines such as diethanolamine (DEA) andtriethanolamine (TEA). The base is preferably added to the reactionmixture after the reaction between the alkanolamine and the carboxylicanhydride has been active stopped by adding water.

An alternative binder composition may be based on a furan resin. Such afuranic binder composition is described in European patent EP0849987.The furanic binder composition is both formaldehyde-free andhydrophilic, thereby offering particular advantages in the context ofthe present invention.

Although preferred embodiments of the invention use a formaldehyde-freebinder, binder systems comprising phenol-formaldehyde (PF), orparticularly phenol-urea-formaldehyde (PUF), with or without dextrosemay also be used where appropriate. These may include Ultra LowFormaldehyde (ULF) binders.

As mentioned above, the binding system preferably comprises a wettingagent. This can be a non-ionic surfactant but preferably the wettingagent is an ionic surfactant. By using the binder described above, thewetting agent is not essential to provide a hydrophilic binder system.Accordingly, adequate water retention and re-saturation properties maybe achieved without the wetting agent. However, the use of a wettingagent is preferred as it is found to increase the speed at which theslab may become saturated.

Preferably, the wetting agent is an anionic surfactant. Suitable anionicsurfactants include salts (including, for example, sodium, potassium,ammonium and substituted ammonium salts such as mono-di- andtriethanolamine salts) of the anionic sulphate, sulphonate, carboxylateand sarcosinate surfactants. Other anionic surfactants includeisethionates such as the acyl isethionates, N-acyl taurates, fatty acidamines of methyl tauride, alkyl succinates and sulfosuccinates, monoesters of sulfosuccinates, di-esters of sulfosuccinates and N-acylsarcosinates. Preferred are anionic sulphate surfactants and anionicsulphonate surfactants, anionic carboxylate surfactants and anionic soapsurfactants.

Particularly preferred are the anionic sulphonate surfactants such aslinear or branched alkyl benzene sulphonates, alkyl ester sulphonates,primary or secondary alkylene sulphonates, olefin sulphonates,sulphonated polycarboxylic acids, alkyl glycerol sulphonates, fatty acylglycerol sulphonates, fatty oleyl glycerol sulphonates and mixturesthereof.

Most preferably the anionic surfactant is a linear alkyl benzenesulphonate in which the alkyl chain has from 5 to 20 carbon atoms. Thesodium and potassium salts are preferred. This type of surfactantprovides particularly beneficial water distribution properties forgrowth substrates of relatively large height and also provides excellentre-saturation properties and does not lead to foaming problems in theirrigation water. Conventional non-ionic surfactants allow the growthsubstrate to take up water, but their water retaining capacity, waterdistribution over height and re-wetting properties are not as good aswith this type of surfactant, preferred in the invention.

Preferably the alkyl chain length is in the range 8 to 16, and morepreferably at least 90% of the chains are in the range 10 to 13 and morepreferably at least 90% (by weight) are in the range 10 to 12.

Preferably the wetting agent comprises a linear alkyl benzene sulphonateand in this case the product is preferably produced by a method in whicha polyol (such as monoethylene glycol) is included with the wettingagent in the mineral fibre product. The weight ratio of linear alkylbenzene sulphonate to monoethylene glycol (or other polyol—for instancepropylene glycol or trimethylolpropane) is preferably 0.3:1 to 3.75:1,preferably 1:1 to 2:1. The polyol is normally evaporated duringsubsequent processing and curing and thus usually only trace amounts, ifany, are present in the final product.

Alternatively, the ionic surfactant may be cationic or zwitterionic.Examples of cationic surfactants include quaternary ammoniumsurfactants. These can, for instance, be selected from mono C6 to monoC16, preferably C6 to C10 N-alkyl or alkenyl ammonium surfactantswherein the remaining N positions are substituted by groups such asmethyl, hydroxyethyl and hydroxypropyl.

Suitable zwitterionic surfactants include derivatives of secondary andtertiary amines, derivatives of heterocyclic secondary and tertiaryamines, or derivatives of quaternary ammonium, quaternary phosphonium ortertiary sulphonium compounds. Betaine and sultaine surfactants areexamples of zwitterionic surfactants.

Preferably the amount (by weight) of ionic surfactant based on theweight of binder (dry matter) is in the range 0.01 to 5%, preferably 0.1to 4%.

The ionic surfactant is present in the mineral fibre product in amountspreferably from 0.01 to 3% (by weight), based on mineral fibre product,more preferably 0.05 to 1%, in particular, 0.1 to 0.8%.

The binder compositions used according to the present invention mayadditionally comprise one or more conventional binder additives. Theseinclude, for instance, curing accelerators such as, e.g.β-hydroxyalkylamides; the free acid and salt forms of phosphoric acid,hypophosphorous acid and phosphonic acid. Other strong acids such asboric acid, sulphuric acid, nitric acid and p-toluenesulphonic acid mayalso be used, either alone or in combination with the just-mentionedacids, in particular with phosphoric acid, hypophosphorous acid orphosphonic acid. Other suitable binder additives are ammonia; silanecoupling agents such as γ-aminopropyltriethoxysilane; thermalstabilisers; UV stabilisers; plasticisers; anti-migration aids;coalescents; fillers and extenders such as clay, silicates and magnesiumhydroxide; pigments such as titanium dioxide; flame retardants;corrosion inhibitors such as thiourea, urea; antifoaming agents;antioxidants; and others.

These binder additives and adjuvants may be used in conventional amountsgenerally not exceeding 20 wt. % of the binder solids. The amount ofcuring accelerator in the binder composition is generally between 0.05and 5 wt. %, based on solids.

Once applied to the mineral fibres, the aqueous binder compositiongenerally has a solids content of from 1 to 20 wt. % and a pH of 5 orgreater.

The mineral fibres employed may be any man-made vitreous fibres (MMVF),such as glass fibres, ceramic fibres, basalt fibres, slag wool, stonewool and others, but are usually stone wool fibres. Stone wool generallyhas a content of iron oxide at least 3% and content of alkaline earthmetals (calcium oxide and magnesium oxide) from 10 to 40%, along withthe other usual oxide constituents of mineral wool. These are silica;alumina; alkali metals (sodium oxide and potassium oxide) which areusually present in low amounts; and can also include titania and otherminor oxides. In general the product can be formed of any of the typesof man-made vitreous fibre which are conventionally known for productionof growth substrates.

The Loss on Ignition (LOI) of the slab is a measure of the amount oforganic material such as binder and wetting agent present. The LOI of adry sample may be measured using section 16 of BS2972, 1989 (Method 1).The LOI is preferably at least 2.5%, preferably up to 5.3%, especiallypreferably 3-4%. In particular, the most preferred LOI is 3.5%. Thepreferred LOI for the slab offers good strength, but with the binderdescribed above plant growth is not negatively affected despite thehigher level of binder.

A higher LOI means the product is stronger. This means it is less likelyto be damaged during use, especially during automated processing, forinstance at a propagation facility. A further advantage of a higherbinder content is that a smoother seed bed/hole can be formed in growthsubstrates such as plugs and blocks that are commonly provided with aseed hole. A smoother seed hole means that the seed is more likely topropagate from the ideal position in the seed bed/hole. The seed isadditionally less likely to bounce out of the desired area, and/or becaught another part of the mineral fibre product. Accurate positioningof seeds leads to greater uniformity of the resulting crop which isadvantageous for the propagator.

The diameter of the fibres within the slab 1 is preferably in the rangeof 2 to 10 μm, more preferably in the range of 3 to 8 μm, andparticularly preferably in the range of 4 to 7 μm. These values mayapply equally to the diameter of the fibres in the block 2 and/or plug4.

In the preferred embodiment, the predominant fibre orientation of thefirst and second layers of the slab 1 is horizontal. This is found toreduce vertical non-uniformity in the water distribution. In thiscontext, horizontal means parallel to the interfacial contact betweenthe first and second layers. Alternative fibre orientations may be usedin the first and/or second layers in other embodiments.

FIG. 4 shows a plant growth system comprising the slab 1, block 2 andplug 4 of FIGS. 1 to 3 and an irrigation device. The irrigation device 6is arranged to provide a solution of water and nutrients to the system,either directly to the block or to the slab. In the preferredembodiment, the irrigation device is arranged to provide water and/ornutrient solution directly to the block 2. Since the block is disposedaway from the drain hole 3 (as described above with reference to FIG.2), solution from the irrigation device must pass more than 50% of thedistance along the slab 1 before reaching the drain hole 3. In otherpreferred embodiments, the irrigation device may provide the water andnutrient solution to the slab 1 directly, but it is preferably arrangedto do so either adjacent to the block or at a distal side of the block 2relative to the drain hole 3.

It is found that an increased distance between the irrigation device 6(i.e. the point at which the water and nutrient solution is provided tothe system) and the drain hole 3 improves the nutrient refreshmentefficiency of the system. This means that as solution is supplied usingthe irrigation device 6 it is not lost through the drain hole 3 butinstead will replace existing liquid in the system. Accordingly, thetotal volume of the slab 1 is refreshed, rather than only a limited partof it.

The irrigation device 6 may be connected to separate nutrient and waterreservoirs, and may be controlled to select the appropriate proportionsof nutrients and water. Alternatively, a single combined nutrient andwater reservoir may be provided such that the irrigation device providesliquid to the system having the same proportions of water and nutrientsas are found in the reservoir.

The control of the irrigation device is preferably effected using acontrol system. The control system may control the irrigation devicesproviding nutrients and water to a plurality of plant growth systemseach comprising a slab 1 upon which a plant-containing block 2 isplaced. The control system may be controlled on the basis of detectedwater, nutrient and/or temperature levels in one or more of the slabs.The locations of the detectors 7 used to detect these levels in oneembodiment are illustrated in FIG. 5. The detectors 7 may be of a knowntype, and will typically comprise a body portion together with one ormore, usually three probes which extend from the body into the slab. Theprobes are typically made from stainless steel or another conductivematerial, and are used to measure the water content and/or electricalconductivity (EC) levels of the substrate by analysing the substrate'stemperature, resistance and/or capacitance. The EC level can be used toinfer the nutrient level within the solution in the slab 1 as theyreflect the ionic content of that solution.

In prior art systems, the detectors 7 are placed on the upper surface ofthe slab 1, with the probes extending vertically through the slab. Thisapproach is intended to provide a measurement which reflects the overallwater or nutrient content across the vertical extent of the slab 1.However, in practice, such probes typically return results which aredisproportionally influenced by the conditions in one or more areas ofthe slab 1, such as in the top portion of the slab. One reason thisdisparity can arise is because of variation in the EC level across theslab 1, which clearly affects the measured electrical properties such asresistance and/or capacitance from which, for example, the water contentis calculated.

Further difficulties arise in prior art approaches due to the number ofblocks 2 usually placed on a slab 1. It is often difficult to findpositions on the slab 1 which are functionally equivalent for each block2, particularly given the inherent asymmetry in the system caused by thelocation of the drain hole 3 at one end of the slab 1.

In the present invention, these difficulties are overcome. Inparticular, FIG. 5 shows that the detectors 7 are disposed on the sideof the slab 1 (i.e. the body portion of the detector 7 is disposedagainst a vertical face of the slab and the probes extend horizontally).This approach is available because of the improved water content and ECdistributions within the slab 1. Since these are substantially uniformin the slab 1 of the preferred embodiment, the horizontal extent of theprobes provides an accurate reading.

Indeed, while the slab 1 of FIG. 5 is illustrated with a plurality ofdetectors 7, this is not the case in all preferred embodiments. Thearray of detectors 7 shown in FIG. 5 allows measurement of the watercontent distribution and EC distribution, and has been used to analysethe slab 1 characteristics, providing results such as those detailedbelow. However, in practice it is found that only a single detector 7may be required. This detector 7 preferably comprises horizontallyextending probes located at a position offset from the block towards thedrain hole 3. In particular, in a preferred embodiment, the detector 7is located at a distance of 200 mm from the drain hole 3 and 100 mm fromthe block 2. The positions of the block 2 and the detector 7 in thiscontext are measured from their central points.

The detectors 7 are used to control the level of water and/or nutrientsprovided to the slab 1 by using a control system such as thatillustrated in FIG. 6. As can be seen from this Figure, the detectors 7observe the data in the slabs 1, and communicate this across a network 8to a control unit 9. The control unit then drives the irrigation devices(drippers) 6 across the network 8 in order to provide water andnutrients to the slabs 1. The control unit 9 can be programmed with adesired irrigation strategy (as discussed in more detail below) and canautomatically ensure that the irrigation is carried out to meet desiredwater levels or nutrient levels in the slab 1. In this way, an automaticcontrol of the irrigation process to provide a desired result isachieved.

Typically, each control system will comprise a large number of slabs 1.There may be detectors 7 placed on every slab 1, or there may bedetectors placed on a selection of the slabs 1 to provide representativeresults. The detectors 1 are fixedly mounted to the slabs 1, in orderthat they can provide results to the control unit 9 at regularintervals. For example, the detectors may provide results at intervalsof one minute, five minutes or another suitable time period. This allowsthe slabs 1 within the system to be constantly monitored so that theycan be irrigated appropriately.

The irrigation devices 6 of the system are controlled to apply aspecific irrigation strategy. This strategy comprises a number ofdistinct phases, designed to steer plants through generative andvegetative growth. As is understood in the art, generative growth refersto a type of growth in which the production of flowers/fruit isencouraged, while during vegetative growth the plant a higher proportionof leaves and other green elements are produced. Generative growth isencouraged when a plant has a relative lack of water and/or nutrients,while vegetative growth is encouraged by a plentiful supply of waterand/or nutrients. Vegetative growth produces the higher increase inoverall biomass of the plant, while generative growth increases theproportion of the growth which contributes to the production of fruit orflowers.

It has been known to take advantage of these different growth types byapplying irrigation strategies such as those shown in FIG. 7A. Accordingto the irrigation strategy, the plant growth substrate is watered eachday in an attempt to reach a desired water content level. The watercontent of the substrate is measured as a percentage of the watercontent of the substrate when the substrate is fully saturated. Thus, avalue of 0% represents a dry substrate, while a value of 100% representsa fully saturated substrate.

FIG. 7A shows the progression of this desired water content of thesubstrate over a year-long cycle. The y-axis shows Water Content as apercentage of the saturated level, while the x-axis shows time measuredin weeks. This time is measured from the point at which the block 2 isplaced on the slab 1. As well as the desired water content, FIG. 7A alsoshows the typical range of achieved water content in the substrates.This range is relatively wide due to the poor control of substrateconditions available using prior art systems.

Firstly, prior to placing the block 2 on the slab 1, the slab 1 istypically saturated or near-saturated with water. This helps to ensurethat when the block 2 is first placed on the slab 1, root growth intothe slab 1 is encouraged. At this point, however, the grower is anxiousto ensure that the plant 5 provides fruit as soon as possible. In orderto achieve this, the grower aims to impart a “generative impulse” (i.e.an impulse to initiate generative growth). This is done during a firstperiod of the irrigation strategy, by reducing the desired water contentdown to a minimum level before increasing it again. The principle isthat the reduction of water content will encourage generative growth ofthe plant and thus the flowering of the plant leading to fruit at theearliest available time.

So, from FIG. 7A it can be seen that during the generative impulse inthis prior art irrigation strategy, the desired water content level ofthe substrate drops from around 95% down to 45%. This significant dropis in part necessary because of the wide range of achieved watercontent, which can be seen in that even after the drop to 45% for thedesired water content, the achieved range extends from around 40% up toaround 55%. Thus, it was considered necessary in order to achieve therequired generative impulse for all plants that the irrigation strategyshould comprise a reduction of desired water content of the magnitudeshown in FIG. 7A.

After the generative impulse is applied, the grower wishes to return theplant to a sustainable phase of predominantly vegetative growth in orderto obtain leaves and plant structure which will support the now growingfruit. Thus, towards the end of the first period of the irrigationstrategy, the desired water content is increased. The desired watercontent level is increased until it reaches a sustainable value at whichit is held substantially constant during a second period of theirrigation strategy.

In the second period, more vegetative growth is encouraged due to thehigher water content in the substrate. The constant level is chosen asaround 80% in order to ensure the correct bias towards vegetativegrowth.

The second period corresponds broadly to the summer season, during whichthe relatively high amount of sunshine causes the plants to transpire ata greater rate. Accordingly, a relatively high proportion of water mustbe provided to the plants. It should be recognised that although growthmay be steered towards vegetative growth during this period more than atother periods, fruit continues to grow, although the rate is controlledby this steering. As the season turns to autumn and then winter, thetranspiration rate reduces. As a result, it is no longer necessary tomaintain the same water content in the substrate. Moreover, there is atthis stage a desire to encourage further fruit growth before the plantreaches the end of the cycle. For both these reasons, the irrigationstrategy may comprise a third period in which the water content level isreduced. The rate of reduction is relatively gradual.

The reduction in water content during the third period encouragesgenerative growth in the plant, and thereby extends the season duringwhich useful fruit can be obtained from the plant.

So, the conventional irrigation strategy of FIG. 7A attempts to steerthe plant between generative and vegetative growth states in order toincrease the yield of fruit obtained from the plant. However, thissteering is found only to be of limited practical effect or utility.Moreover, there is difficulty transferring between the different watercontent levels in the time period which would be preferred. For example,increasing the water content level from the minimum level during thefirst period to the constant level of the second period is timeconsuming. If it were attempted to increase this level more quickly byproviding more water then it is found that the level of water spilledfrom the plant is excessive and problematic. Moreover, because of thebroad range of achieved water content levels, there is difficulty inaccurately steering the plant to the preferred level of generative orvegetative growth.

In contrast, an irrigation strategy for use in accordance with apreferred embodiment of the present invention is shown in FIG. 7B. Ithas surprisingly been found that in the context of a plant growthsubstrate comprising a slab and only a single block, as described above,the parameters of the irrigation strategy can be greatly changed whilestill achieving the necessary generative and vegetative effects. As willbe demonstrated below, this offers improved yield from the plant, whileat the same time avoiding unnecessary use of resources such as waterand/or nutrients.

The preferred irrigation strategy shown in FIG. 78 comprises the first,second and third periods described above. However, there is asubstantial difference in the values that are used to operate theirrigation strategy during these periods. In particular, the differencebetween the desired water content at the minimum point during the firstperiod and the constant level during the second period is significantlyreduced. This difference between these two levels in the strategy shownin FIG. 7B is 15%, as compared with a difference of 35% in the strategyof FIG. 7A. In general, it is preferred that the difference is less than25%, more preferably less than 20%.

Despite this smaller difference, it is found that a sufficiently stronggenerative impulse can be imparted to the plants, due to the fact that asingle block system is used in combination with a slab of an appropriatesize, as described above. As can be seen from FIG. 7B, this allows thevariation of the actual achieved water level from the desired waterlevel to be significantly smaller than was the case previously.

The small variation in the desired water content level required for thegenerative impulse and subsequent sustainable growth during the secondperiod offers a number of advantages. In particular, the time requiredto go between substantially generative and substantially vegetativegrowth is much reduced, allowing the grower to obtain fruitsignificantly earlier in the season. This is reflected in the fact thatthe second period of constant water level is initiated at approximatelyweek 15 in the strategy shown in FIG. 7A, whereas the same period ofgrowth is initiated around week 10 in the strategy of FIG. 78. Thisrepresents a significant advantage to the grower, who is able to obtainfruit earlier, at a time of year where it is relatively costly.

FIGS. 7A and 7B show the yearly progression of the desired water contentlevel. However, it should be recognised that there are also variationsin the water content level each day, according to the time at whichirrigation is applied and the level of transpiration of the plant (whichwill be affected by the hours of sunlight and other criteria).Therefore, it should be understood that the desired water contentreferred to with respect of the irrigation strategies above is thedesired water content immediately after irrigation each day. That is,when the plants are provided with water, this is done in an attempt toreach the desired water content as referred to above.

In the example of FIG. 7B, the minimum desired water content levelduring the first period is around 60%, while the constant desired watercontent level of the second period is around 70%. More generally, it ispreferred that the minimum level is at least 50%, and more preferably atleast 60%. Similarly, the constant level is preferably less than 80%,and in particularly preferred embodiments is in the range 73% to 78%.

The skilled person will recognise that the specific values and thelengths of the time periods given during the strategy of FIG. 78 may bevaried while remaining in accordance with the present invention. Forexample, variations may be carried out on the basis of the plants thatare grown or climatic conditions. Nevertheless, it is a characteristicof preferred irrigation strategies that steering between generative andvegetative states can be achieved by relatively small changes in desiredwater content.

The difference between the irrigation strategies of FIGS. 7A and 7B canbe understood further with reference to FIGS. 8A to 8D. These Figuresshow the results of a trial between 17 Aug. 2011 and 1 Nov. 2011 inwhich a comparison was made between an irrigation strategy according tothe preferred embodiment such as that of FIG. 7B and a conventionalirrigation strategy such as that shown in FIG. 7A. Each type of strategywas applied to an array of nine plant growth systems, each comprising asingle slab and a single plant-containing block as described above, andresults were compared. Each array of plant growth systems shared asingle gutter to receive drained liquid from their drain holes. Thevalues shown in FIGS. 8A to 8D represent the second period of thestrategy, during which the desired water content is maintainedrelatively constant.

FIG. 8A shows the daily volume of water and nutrient solution applied tothe array of nine plant growth systems in both irrigation strategies. Ascan be seen from FIG. 8A, the average “Gift” (defined as the volume ofwater and nutrient solution provided per gutter per day) issignificantly lower for the preferred strategy of FIG. 7B than for theconventional strategy of FIG. 7A. FIG. 86 shows the daily drain ofliquid through the drain hole for the nine plant growth systemsassociated with the gutter. Again, on average this drain issignificantly lower for the preferred irrigation strategy than for theconventional irrigation strategy.

The water and nutrient solution was provided to each plant growth systemin multiple discrete “trickle sessions” each day. FIG. 8C illustratesthe number of trickle sessions and the volume of liquid at each sessionduring each day in the two irrigation strategies. The values of theseparameters are adjusted through the irrigation process in dependence onfactors such as climatic conditions, the levels of drain andmeasurements of plant growth. Given the dependence on the climate, theparticular strategy shown in the example of FIG. 8C reflects thetransition from summer to autumn during the period over which the trialwas run. Particularly, as the level of sunlight and average temperaturereduced, the amount of water and nutrient solution required alsoreduced. If the irrigation period had covered a transition from winterto spring, for example, one would have found a different trend in thevolume of liquid provided to the plant growth systems.

FIG. 8D summarises the results shown in FIGS. 8A to 8C. In particular,the average gift, drain and uptake is given in litres for the array ofplant growth systems for each of the irrigation strategies. Furthermore,the percentage of the gift which is taken by the plants (i.e. the uptakeefficiency) and the percentage which is lost (i.e. the drain) is shownfor each irrigation strategy. We can see from these figures, that theuptake efficiency is significantly increased using the preferredstrategy. Moreover, the absolute drain, as well as the drain percentage,is substantially reduced using the preferred strategy. The preferredstrategy therefore substantially reduced wastage. Moreover, the smallerabsolute uptake which occurs using the preferred strategy reduces energyuse for transpiration and also increases the applicability of thestrategy in closed greenhouse systems.

The achieved progression of the water content in the slab 1 when using aplant growth system according to a preferred embodiment was alsomeasured in a further study over a longer time frame. The results areillustrated in FIG. 9. In FIG. 9, it can be seen that minimum watercontent of around 60% was achieved around 5 weeks from the beginning ofthe study. This minimum water content was found to provide the requiredgenerative impulse, and the water content level was subsequently raisedto around 70% and remained in that region before gradually reducinglater in the year. This 10% difference between minimum and constantlevels was found to provide the necessary steering for the plant, and itwas understood from the trial that a difference of 15% or less providessignificant benefits.

FIG. 10 onwards further demonstrate the advantages of the presentinvention. In particular, a comparison of a plant growth systemfabricated in accordance with a preferred embodiment of the presentinvention and a prior art plant growth system was undertaken. FIG. 10Billustrates the embodiment of the present invention used for thiscomparison while FIG. 10A illustrates the plant growth system accordingto the prior art used for the comparison. The plant growth systems wereused to grow tomato plants. As can be seen from the figures, each systemcomprised a single drain hole at one end of the slab. The prior artsystem comprises three separate blocks placed on the upper surface ofthe slab, whereas the embodiment of the invention comprises only asingle block.

The slab of the preferred embodiment shown in FIG. 10B has dimensions of450 mm*150 mm*100 mm (length*width*height) while the block hasdimensions of 100 mm*100 mm*65 mm (length*width*height). The block islocated 300 mm along the slab away from the drain hole (as measured fromthe centre of the block) and an irrigation device is provided to delivera water and nutrient solution to the block at a distal side of the blockto the drain hole.

The slab of the prior art shown in FIG. 10A has dimensions of 1330mm*195 mm*75 mm (length*width*height) while the blocks have dimensionsof 100 mm*100 mm*65 mm (length*width*height). The blocks are located atpositions of 150 mm to 200 mm, 650 mm to 700 mm and 1100 to 1150 mmalong the slab away from the drain hole (as measured from the centre ofthe block) and irrigation devices are provided for each block to delivera water and nutrient solution to the block at a distal side of the blockto the drain hole.

Identical new and conventional irrigation strategies were applied to theblocks of the plant growth systems of FIGS. 10A and 10B, and variousproperties of the system were measured. In particular, both watercontent (WC) and electrical conductivity (EC), together with thedistribution of these properties, were measured.

It is found that the uniformity of both the water content and theelectrical conductivity is improved in the preferred embodiment ascompared to the prior art. For example, FIG. 11 shows the variation inthe measured water content and electrical conductivity for the preferredembodiment and the prior art under preferred and conventional irrigationstrategies. The variation is measured between the upper layer and thelower layer of the slab. For both water content and electricalconductivity, and under both irrigation strategies, the variation isreduced using the preferred embodiment. The values used are the averagevariations exhibited during the trial. The reduced variation using thepreferred embodiment represents an increased uniformity within the slab.

The reduced variation in water content has a particular effect on rootgrowth. Since previous approaches typically resulted in a wetter bottomregion of the slab 1, root growth was typically encouraged towards thebottom of the slab 1. By using slabs 1 according to the preferredembodiment of the present invention, it has been found that asignificantly higher proportion of root growth occurs in the top of theslab. This results in a healthier plant, which can moreover be moreclosely controlled because new irrigation (for example, changing thewater content or EC) reaches the root zone more quickly as it is closerto the irrigation device itself.

The improved water retention, water distribution and electricalconductivity (nutrient) distribution lead to improved growing conditionsfor the plants growing in the plant growth systems. Ultimately, thisleads to an improved yield, as illustrated in FIG. 12.

In FIG. 12, the yield of red tomato plants achieved by the preferredembodiments is shown in terms of number and weight. Values arenormalised such that the yield of the prior art gives a value of 100.The yield is presented for an average of both irrigation strategies andfor the preferred and conventional irrigation strategies independently.As can be seen, in all circumstances, the yield of the preferredembodiment is superior to that of the prior art. Moreover, it is notablethat the preferred embodiment offers particular advantages for apreferred strategy and in terms of the weight of fruit and/or flowersproduced.

The advantages of the preferred embodiment are not limited to animproved yield, however. The ability to take advantage of the preferredgrowth strategy also reduces the amount of water and nutrients that mustbe provided to the plant growth system. Moreover, superior waterretention means that less of this fluid is lost through the drain hole.Costs are reduced in terms of water and nutrient supply and in terms ofthe processing costs required to environmentally dispose of or re-usedrained fluid. Thus, the approach taken by the preferred embodimentcombines an improved yield with lower costs. This is achieved in lightof the recognition that close control of the conditions of individualplants can be realised with the preferred plant growth systems describedherein.

In addition to advantages in respect of the improved water retention,water distribution and nutrient distribution, the present invention alsoprovides advantages in terms of nutrient refreshment efficiency. Thenutrient refreshment efficiency reflects the rate at which old nutrientsin the substrate can be replaced by new nutrients provided to thesubstrate in solution. It is preferable that nutrients can be refreshedin this way as efficiently as possible.

The advantages of the present invention were also observed during thefurther study referred to above with reference to FIG. 9. Overapproximately a year, two preferred embodiments of the present inventionwere subjected to an irrigation strategy approximately in line with thatreflected in FIG. 9. The first preferred embodiment comprised thepreferred hydrophilic, formaldehyde-free binder system as describedabove, while the second preferred embodiment used an alternative bindersystem. The results were compared with those from a prior art plantgrowth system such as that shown in FIG. 10A above. The desiredirrigation strategy applied to the prior art system was the same,although the difficulty in controlling water content accurately in thatsystem lead to a slight variation in measured water content over theperiod of the study.

FIGS. 13A and 138 illustrate the results of this study in terms of thetotal production of fruit achieved. FIG. 13A shows the total productionof all three plant growth systems, and the development of this over theperiod of the study. In FIG. 13A, the unbroken line represents theresults for the plant growth system of the first preferred embodimentreferred to as Example A using a preferred binder as described abovewhile the dashed line represents the results for the second preferredembodiment referred to as Example B. Finally, the dotted line representsthe production achieved with the prior art system referred to as ExampleC. FIG. 13B brings the differences between the various systems into evengreater relief by showing the differences for the first preferredembodiment (unbroken line—Example A) and second preferred embodiment(dashed line—Example B) compared to the prior art system.

It can be seen from FIGS. 13A and 13B that the performance of thepreferred embodiments was significantly improved over that of the priorart system. Furthermore, the benefits of the improved binder system ofthe first preferred embodiment are also clear. Over 47 weeks, the totalproduction per unit area for the first preferred embodiment was 63.5kg/m2, that of the second preferred embodiment was 62.2 kg/m2, and thatof the prior art system was 58.0 kg/m2.

FIG. 14 shows the advantage of an embodiment of the present inventioncompared to a prior art substrate (as reflected in FIGS. 10A and 108above) in terms of improved nutrient refreshment efficiency. In thistrial, each slab was initially provided with a nutrient solution havingan EC of 5. Once the EC of 5 was established in the substrate, thesubstrate was irrigated with a solution having an EC of 2. It can beappreciated that if the solution within the substrate is replaced by thenew solution of EC 2 then the EC of the substrate itself will also tendto a value of 2. The faster the rate at which this happens, the moreefficient is the replacement of nutrients within the solution.

As can be seen from FIG. 14, the preferred embodiment of FIG. 10B offersa faster change in EC than the prior art approach of FIG. 10A. Thisdemonstrates the improved nutrient refreshment efficiency of thepreferred embodiment.

Improvements in nutrient refreshment efficiency offer a number ofadvantages. In particular, the unwanted build up of nutrients in areasof the substrate can be avoided, and the nutrient level can be closelycontrolled according to the requirements of the plant.

Further advantages in terms of the control of EC levels can be realisedthrough the preferred placement of the block 2 upon the slab 1. Evidenceof this can be found in FIGS. 15A and 15B. In each Figure, measurementsof EC were taken at multiple distances from the drain hole at one end ofthe slab 1 and at multiple heights.

In FIG. 15A, the block 2 was placed at 20 cm from the drain hole on ablock of length 50 cm. Measurements were taken at heights of 5.0 cm,3.75 cm, 2.5 cm and 1.25 cm from the bottom of the block 1. For eachdistanced from the drain hole, measurements are illustrated for each ofthese heights in the order from left to right in FIG. 15A from highestto lowest.

In FIG. 15B, the block 2 was placed at 25-30 cm from the drain hole on ablock of length 40 cm. Measurements were taken at heights of 6.8 cm, 5.1cm, 3.4 cm and 1.7 cm from the bottom of the block 1. For each distancedfrom the drain hole, measurements are illustrated for each of theseheights in the order from left to right in FIG. 15B from highest tolowest.

The variation in EC levels was found to be significantly greater in theexamples shown in FIG. 15A than in that shown in FIG. 15B. Moreparticularly, the standard deviation of EC was found to be around 0.73in the example of FIG. 15A against a significantly smaller standarddeviation of 0.37 for FIG. 15B. The figures illustrate improveduniformity both a differing heights and at differing distances from thedrain hole for the example of FIG. 15B in which the block is placed over50% of the length of the block away from the drain hole.

Variations and modifications to the embodiments described above will beapparent to the skilled person. Such variations and modifications mayinvolve equivalent and other features which are already known and whichmay be used instead of, or in addition to, features described herein.Features that are described in the context of separate embodiments maybe provided in combination in a single embodiment. Conversely, featureswhich are described in the context of a single embodiment may also beprovided separately or in any suitable sub-combination.

It should be noted that the term “comprising” does not exclude otherelements or steps, the term “a” or “an” does not exclude a plurality, asingle feature may fulfil the functions of several features recited inthe claims and reference signs in the claims shall not be construed aslimiting the scope of the claims. It should also be noted that theFigures are not necessarily to scale; emphasis instead generally beingplaced upon illustrating the principles of the present invention.

1. A plant growth method, comprising: providing a plant growth substratecomprising an MMVF slab having a volume in the range 3 to 20 litres anda single MMVF block containing one or more plants on a first subsurfaceof the MMVF slab; providing the plant growth substrate with water duringgrowth of the one or more plants according to an irrigation strategywhich defines a desired water content in the slab, wherein theirrigation strategy comprises a first period during which the desiredwater content is reduced to a minimum level before increasing and asecond period during which the desired water content is maintained at asubstantially constant level, wherein the difference between the minimumlevel and the constant level expressed as a percentage of the watercontent required to saturate the plant growth substrate is less than orequal to 25%.
 2. A method according to claim 1, wherein the irrigationstrategy further comprises a third period during which the desired watercontent is reduced.
 3. A method according to claim 1, wherein thedifference between the minimum level and the constant level expressed asa percentage of the water content required to saturate the plant growthsubstrate is less than or equal to 20%.
 4. A method according to claim3, wherein the difference between the minimum level and the constantlevel expressed as a percentage of the water content required tosaturate the plant growth substrate is in the range of 10% to 15%.
 5. Amethod according to claim 1, wherein the minimum level expressed as apercentage of the water content required to saturate the plant growthsubstrate is at least 50%.
 6. A method according to claim 5, wherein theminimum level expressed as a percentage of the water content required tosaturate the plant growth substrate is at least 60%.
 7. A methodaccording to claim 6, wherein the constant level expresses as apercentage of the water content required to saturate the plant growthsubstrate is 75% or less.
 8. A method according to claim 1, wherein thedesired water content is reduced to the minimum level within 7 weeks ofcommencement of the irrigation strategy.
 9. A method according to claim1, wherein the desired water content reaches the substantially constantlevel within 12 weeks of commencement of the irrigation strategy.
 10. Amethod according to claim 1, further comprising providing nutrients tothe plant growth substrate.
 11. A method according to claim 9, whereinthe step of providing nutrients to the plant growth substrate is carriedout in dependence on monitored nutrient level within the plant growthsubstrate.
 12. A method according to claim 1, wherein the MMVF slabcomprises a hydrophilic binder system.
 13. A method according to claim1, wherein the MMVF slab comprises a binder system comprising an organicbinder selected from formaldehyde-free binders.
 14. A method accordingto claim 1, wherein the MMVF slab comprises a first layer of MMVF ininterfacial contact with a second layer of MMVF, the first layer havinga greater density than the second layer.
 15. A method according to claim14, wherein the first layer of MMVF has a density in the range 40 to 90kg/m³ and the second layer of MMVF has a density in the range 35 to 85kg³.